Artificial lighting systems for closed environments often aim at improving the visual comfort experienced by users. For example, lighting units are known for simulating natural lighting, specifically sunlight illumination, that provide dichroic light to be emitted from a dichroic light exiting surface, where the dichroic light comprises a directional light portion of direct light having a first correlated color temperature (CCT) and a diffused light portion of diffused light having a second CCT. The direct light radiates essentially along a local main direction, wherein the local main direction corresponds to a luminous intensity peak in the angular luminous intensity distribution of the direct light emitted at a specific location of the light exiting surface. In other words, inter alia local main direct light rays originate from specific locations in respective local main direction. In contrast, the diffused light has in particular for natural lighting imitation a second correlated color temperature, which is larger than the first correlated color temperature. That sky imitating light radiates with a local Lambertian-like angular luminous intensity distribution from specific locations of the light exiting surface.
Exemplary embodiments of such lighting systems using, for example, Rayleigh-like diffusing layers are disclosed in several applications such as WO 2009/156347 A1, WO 2009/156348 A1, WO 2014/076656 A1, and WO 2015/172821 A1 filed by the same applicants. The disclosed lighting systems use a light source producing visible light, and a panel containing nanoparticles used in transmission or reflection. During operation of those lighting systems, the panel receives the light from the light source and acts as a so-called Rayleigh diffuser, namely it diffuses incident light similarly to the earth atmosphere in clear-sky conditions. Specifically, the disclosed concepts refer to directional light with lower correlated color temperature (CCT), which corresponds to sunlight, and diffuse light with larger CCT, which corresponds to the light of the blue sky.
In further embodiments such as those disclosed in WO 2014/075721 A1, the un-published international patent application PCT/EP2015/077169, and the not yet published international patent application PCT/EP2015/069790 filed by the same applicants on 28 Aug. 2016, the concepts of direct light with lower CCT and diffused light with larger CCT are implemented in a linear configuration and in a compact setup using e.g. a one-dimensionally curved mirror and light guide configuration, respectively. It is noted that WO 2014/075721 A1 discloses further a coffered ceiling structure that is used to mask modulations within the artificial sky, while maintaining direct “sunlight” illumination.
The contents of the above mentioned disclosures are incorporated herein by reference.
To provide for a sun-like impression, the light sources may be designed for a sun-like perception such as disclosed in WO 2015/172794 A1 filed by the same applicants. As disclosed therein, a detailed analysis and a plurality of optical measures were implemented to achieve the desired sun-like perception of the aperture of the light source.
The herein disclosed concepts are in particular directed at providing lighting systems that can achieve similarly the simulation of natural lighting, specifically sunlight illumination, but have reduced requirements of the perceptive features of the light source.
Thus, the present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems.